Pfizer Handbook of Microbial Metabolites 



234 



shown below could be envisaged as derivatives of a common 

 precursor chain, which is laid down upon the enzyme surface in 

 different patterns before cyclization.^^ 



O 



It is likely that the dianthraquinones are formed by oxidative 

 phenoUc radical coupling, e.g.:* 



HO O OH 

 Skyrin 



^'' A. J. Birch, private communication. 



* See addendum for evidence to the contrary. 



